Polyester fiber

ABSTRACT

Polyester fibers comprising a copolyester which simultaneously satisfies the following respective requirements (a) to (c),  
     (a) a terephthalic acid component in an amount of 0 to 100 mol % and a 2,6-naphthalenedicarboxylic acid component in an amount of 100 to 0 mol % respectively based on the whole dicarbxylic acid component, wherein the total amount, of the terephthalic acid component and the 2,6-naphthalenedicarboxylic acid component, accounts for 90 mol % or more based on the whole dicarboxylic acid component,  
     (b) a trimethylene glycol component accounts for 0 to 100 mol % and a 1,4-cyclohexanedimethanol component accounts for 100 to 0 mol % respectively based on the whole glycol component, wherein the total amount, of the trimethylene glycol component and the 1,4-cyclohexanedimethanol component, accounts for 90 mol % or more based on the whole glycol component and  
     (c) the sum total value of mol % of the 2,6-naphthalenedicarboxylic acid component and mol % of the 1,4-cyclohexanedimethanol component is 2 mol % or more.

TECHNICAL FIELD

[0001] The present invention relates to polyester fibers and moreparticularly it relates to polyester fibers having resistances tohydrolysis and fatigue from flexing at high levels and suitably usablefor applications of papermaking canvas, tire cord and sterilizedfabrics.

BACKGROUND ART

[0002] As well known, copolyesters have widely been used for fibers,resins, films or the like due to excellent performances thereof.Especially, polyester fibers are excellent in dimensional stability,heat, chemical and light resistances and the like and utilized invarious fields regardless of clothing and non-clothing uses.

[0003] In the situation, polyester fibers have recently been utilizedeven for papermaking canvas such as dryer canvas, tire cord andsterilized fabrics such as medical clothes from the viewpoint ofexcellence in strength and resistance to fatigue from flexing. Amongthem, high resistances to fatigue and hydrolysis sufficient to withstanduses at high temperature and humidity are required in the applicationsof the dryer canvas and sterilized fabrics. The copolyesters, however,have problems that the lowering of molecular weight and the like arecaused by hydrolysis at high temperature and humidity due to chemicalcharacteristics thereof and the copolyester is resultantly unsuitablefor long-term uses at high temperature and humidity.

[0004] In order to solve the problems, for example, JP-A No. 54-6051(1976) and JP-A No. 3-104919 (1991) (hereinafter, JP-A means JapaneseUnexamined Patent Publication) propose methods for adding an epoxycompound or a carbodiimide compound as methods for reducing the terminalcarboxyl group concentration of polyethylene terephthalate. Althoughresistance to hydrolysis is improved to some extent according to themethods, the copolyester are incapable of withstanding long-term usesand the problems have not yet been solved.

[0005] On the other hand, JP-A No. 8-120521 (1996) proposes filamentsusing a polytrimethylene terephthalate as a method for raising theresistance to fatigue from flexing. Although resistances to both fatiguefrom flexing and hydrolysis are considerably improved, the resistance ofthe filaments to hydrolysis for long-term and continuous uses at hightemperature and humidity has not yet reached a sufficient level due to alow glass transition point of the polytrimethylene terephthalate.

DISCLOSURE OF THE INVENTION

[0006] It is an object of the present invention to solve the problemsheretofore possessed by the above prior art and to provide polyesterfibers having resistances to both hydrolysis and fatigue from flexingwhich are capable of withstanding long-term and continuous uses at hightemperature and humidity.

BEST MODE FOR CARRYING OUT THE INVENTION

[0007] The mode for carrying out the present invention will be detailedhereinafter.

[0008] In the present invention, it is necessary for a copolyester whichis formed into the polyester fibers to simultaneously satisfy thefollowing respective requirements (a) to (c).

[0009] (a) a terephthalic acid component in an amount of 0 to 100 mol %and a 2,6-naphthalenedicarboxylic acid component in an amount of 100 to0 mol % respectively based on the whole dicarboxylic acid component,wherein the total amount, of the terephthalic acid component and the2,6-naphthalenedicarboxylic acid component, accounts for 90 mol % ormore based on the whole dicarboxylic acid component,

[0010] (b) a trimethylene glycol component accounts for 22 to 100 mol %and a 1,4-cyclohexanedimethanol component accounts for 78 to 0 mol %respectively based on the whole glycol component, wherein the totalamount, of the trimethylene glycol component and the1,4-cyclohexanedimethanol component, accounts for 90 mol % or more basedon the whole glycol component and

[0011] (c) the sum total value of mol % of the2,6-naphthalenedicarboxylic acid component and mol % of the1,4-cyclohexanedimethanol component is 2 mol % or more.

[0012] The respective requirements (a) to (c) in the present inventionwill be detailed hereinafter.

[0013] When the total amount of the terephthalic acid component and the2,6-naphthalenedicarboxylic acid component is less than 90 mol % basedon the whole dicarboxylic acid component, the resistances to hydrolysisand heat, hand touch and the like of the resulting fibers are lowered.

[0014] When the 1,4-cyclohexanedimethanol component is not contained asthe glycol component of the copolyester in the present invention, thecase where the amount of the terephthalic acid component is 98 mol % ormore and/or the amount of the 2,6-naphthalenedicarboxylic acid componentis less than 2 mol % is unfavorable because the resistance of theresulting fibers to hydrolysis becomes insufficient.

[0015] As to the amounts of the terephthalic acid component and the2,6-napthalenedicarboxylic acid component, it is preferable to make theterephthalic acid component account for 5 to 95 mol % and the2,6-napthalenedicarboxylic acid component account for 95 to 5 mol % andkeep the total amount of the terephthalic acid component and2,6-naphthalenedicarboxylic acid component within the range of 92 mol %or more based on the whole dicarboxylic acid component and it is morepreferable to make the terephthalic acid component account for 8 to 92mol % and the 2,6-naphthalenedicarboxylic acid component account for 92to 8 mol % and keep the total amount of the terephthalic acid componentand the 2,6-naphthalenedicarboxylic acid component within the range of95 mol % or more based on the whole dicarboxylic acid component.

[0016] When the total amount of the trimethylene glycol component andthe 1,4-cyclohexanedimethanol component is less than 90 mol % based onthe whole glycol component, the resistances to hydrolysis and heat, handtouch and the like of the resulting fibers are lowered.

[0017] When the 2,6-naphthalenedicarboxylic acid component is notcontained as the dicarboxylic acid component of the copolyester in thepresent invention, the case where the amount of the trimethylene glycolcomponent is less than 22 mol % and/or the amount of the1,4-cyclohexanedimethanol component is larger than 78 mol % isunfavorable because the resulting fibers have hard hand touch and themelting point is increased to lower the molding processability.Furthermore, the resistance of the resulting fibers to hydrolysisbecomes insufficient if the amount of the trimethylene glycol componentis 98 mol % or more and/or the amount of the 1,4-cyclohexanedimethanolcomponent is less than 2 mol %.

[0018] As to the amounts of the trimethylene glycol component and the1,4-cyclohexanedimethanol component, it is preferable to make thetrimethylene glycol component account for 22 to 95 mol % and the1,4-cyclohexanedimethanol component account for 78 to 5 mol % and keepthe total amount of the trimethylene glycol component and the1,4-cyclohexanedimethanol component within the range of 92 mol % or morebased on the whole glycol component and it is more preferable to makethe trimethylene glycol component account for 22 to 92 mol % and the1,4-cyclohexanedimethanol component account for 78 to 8 mol % and keepthe total amount of the trimethylene glycol component and the1,4-cyclohexanedimethanol component within the range of 95 mol % or morebased on the whole glycol component.

[0019] In addition, it is necessary for the sum total value of mol % ofthe 2,6-naphthalenedicarboxylic acid component and mol % of the1,4-cyclohexanedimethanol component in the copolyester of the presentinvention to be 2 mol % or more. The object of the present invention canonly be achieved by the sum total value kept within the range.

[0020] Components other than the terephthalic acid component,2,6-naphthalenedicarboxylic acid component, trimethylene glycolcomponent and 1,4-cyclohexanedimethanol component may be copolymerizedwith the copolyester formed into the polyester fibers of the presentinvention within the range so as not to deteriorate characteristics ofthe copolyester, preferably within the range of 5 mol % or less based onthe whole dicarboxylic acid component.

[0021] Examples of the copolymerization component include aromaticdicarboxylic acids such as isophthalic acid, o-phthalic acid,diphenyldicarboxylic acid, diphenyl etherdicarboxylic acid, diphenylsulfonedicarboxylic acid, benzophenonedicarboxylic acid,phenylindanedicarboxylic acid, a 5-sulfoxyisophthalic acid metal salt ora 5-sulfoxyisophthalic acid phosphonium salt; aliphatic glycols such asethylene glycol, tetramethylene glycol, pentamethylene glycol,hexamethylene glycol, octamethylene glycol, decamethylene glycol,neopentylene glycol, diethylene glycol, triethylene glycol, polyethyleneglycol, polytetramethylene glycol or cyclohexanediol; alicyclic glycolssuch as 1,4-cyclohexanediol; aromatic glycols such as o-xylylene glycol,m-xylylene glycol, p-xylylene glycol, 1,4-bis(2-hydroxyethoxy)benzene,1,4-bis(2-hydroxyethoxyethoxy)benzene,4,4′-bis(2-hydroxyethoxy)biphenyl,4,4′-bis(2-hydroxyethoxyethoxy)biphenyl, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, 2,2-bis[4-(2-hydroxyethoxyethoxy)phenyl]propane,1,3-bis(2-hydroxyethoxy)benzene, 1,3-bis(2-hydroxyethoxyethoxy)benzene,1,2-bis(2-hydroxyethoxy)benzene, 1,2-bis(2-hydroxyethoxyethoxy)benzene,4,4′-bis(2-hydroxyethoxy)diphenyl sulfone or4,4′-bis(2-hydroxyethoxyethoxy)diphenyl sulfone and diphenols such ashydroquinone, 2,2-bis(4-hydroxyphenyl)propane, resorcinol, catechol,dihydroxynaphthalene, dihydroxybiphenyl or dihydroxydiphenyl sulfone.The components may be used alone or in combination of two or more kindsthereof.

[0022] The glass transition temperature of the copolyester formed intothe fibers in the present invention is preferably 45° C. or above. Whenthe glass transition temperature is 45° C. or above, the resistance tohydrolysis is more raised. The range of the glass transition temperatureis more preferably 46° C. or above, especially preferably 48° C. orabove.

[0023] When the glass transition temperature is too high, themoldability of the polymer is lowered. Therefore, the glass transitiontemperature may be usually 85° C. or below and is preferably 80° C. orbelow.

[0024] The copolyester formed into the polyester fibers of the presentinvention has a terminal carboxyl group concentration preferably withinthe range of 30 eq/ton or below. When the terminal carboxyl groupconcentration is within the range, the resistance of the fibers tohydrolysis is more improved. The terminal carboxyl group concentrationis more preferably within the range of 25 eq/ton or below, especiallypreferably within the range of 20 eq/ton or below.

[0025] A bisoxazoline compound in an amount of 0.05 to 5% by weightbased on the copolyester is preferably added and uniformly mixed andmelt spinning is then preferably carried out when the copolyester usedin the present invention is melt spun and formed into the polyesterfibers. When the amount of the added bisoxazoline compound is within therange, the terminal carboxyl group concentration of the resultingpolyester fibers becomes far lower to resultantly take effect on thesuppression of the lowering of the intrinsic viscosity, an improvementin the resistance to hydrolysis and the like without increasing thedegree of polymerization of the copolyester too much and lowering themelt moldability or without lowering the resistance of the resultingpolyester fibers to heat. The amount of the added bisoxazoline compoundis more preferably within the range of 0.07 to 4% by weight, especiallypreferably within the range of 0.1 to 3% by weight.

[0026] Examples of the bisoxazoline compound herein include2,2′-bis(2-oxazoline), 2,2′-bis(4-methyl-2-oxazoline),2,2′-bis(4,4-dimethyl-2-oxazoline), 2,2′-bis(4-ethyl-2-oxazoline),2.2°-bis(4,4′-diethyl-2-oxazoline), 2,2′-bis(4-propyl-2-oxazoline),2,2′-bis(4-butyl-2-oxazoline), 2,2′-bis(4-hexyl-2-oxazoline),2,2′-bis(4-phenyl-2-oxazoline), 2,2′-bis(4-cyclohexyl-2-oxazoline),2,2′-bis(4-benzyl-2-oxazoline), 2,2′-p-phenylenebis(2-oxazoline),2,2′-m-phenylenebis(2-oxazoline), 2,2′-o-phenylenebis(2-oxazoline),2,2′-p -phenylenebis(4-methyl-2-oxazoline),2,2′-p-phenylenebis(4,4-dimethyl-2-oxazoline),2,2′-m-phenylenebis(4-methyl-2-oxazoline),2,2′-m-phenylenebis(4,4-dimethyl-2-oxazoline),2,2′-ethylenebis(2-oxazoline), 2,2′-tetramethylenebis(2-oxazoline),2,2′-hexamethylenebis(2-oxazoline), 2,2′-octamethylenebis(2-oxazoline),2,2′-deccamethylenebis(2-oxazloine),2,2′-ethylenebis(4-methyl-2-oxazoline),2,2′-tetramethylenebis(4,4-dimethyl-2-oxazoline), 2,2′-9,9′-diphenoxyethanebis(2-oxazoline), 2,2′-cyclohexylenebis(2-oxazoline),2,2′-diphenylenebis(2-oxazoline) and the like. Among them,2,2′-bis(2-oxazoline) is most preferred from the viewpoint of reactivitywith the copolyester.

[0027] Further, one kind of the bisoxazoline compound described abovemay be used alone or two or more kinds may be used in combinationinsofar as the bisoxazoline compound is effective in achieving theobject of the present invention.

[0028] Although methods for adding the bisoxazoline compound to thecopolyester are not especially restricted when the bisoxazline compoundis added to the copolyester in the present invention, there arepreferably adopted methods for dissolving the bisoxazoline compound, forexample, in an organic solvent unreactive with the bisoxazoline compoundand adding the bisoxazoline compound to polyester chips or a polyesterin a molten state and mixing the bisoxazoline compound with thepolyester chips or the polyester in the molten state, methods for addingthe bisoxazoline compound kept in a powder state to the polyester chipsor the polyester in the molten state and mixing the bisoxazolinecompound with the polyester chips or the polyester in the molten state,methods for premixing the bisoxazoline compound in a polyester, forexample, polytrimethylene terephthalate or polyethylene terephthalate soas to provide a high concentration and mixing the resulting master chipswith the polyester chips without adding the compound in chip states andthe like.

[0029] When the copolyester used in the present invention is melt spunand formed into the polyester fibers, a polycarbodiimide compound in anamount within the range of 0.05 to 5% by weight based on the copolyesteris preferably added and uniformly mixed with the copolyester. When theamount of the added polycarbodiimide compound is within the range, theterminal carboxyl group concentration of the resulting polyester fibersbecomes far lower to resultantly take effect on the suppression of thelowering of the intrinsic viscosity, an improvement in the resistance tohydrolysis and the like without increasing the degree of polymerizationof the copolyester too much and lowering the melt moldability or withoutlowering the resistance of the resulting polyester fibers to heat. Theamount of the added polycarbodiimide compound is preferably within therange of 0.07 to 4% by weight, especially preferably within the range of0.1 to 3% by weight.

[0030] Poly(2,4,6-triisopropylphenyl)-1,3-carbodiimide is most preferredas the polycarbodiimide compound from the viewpoint of reactivity withthe copolyester.

[0031] Although methods for adding the polycarbodiimide compound to thecopolyester are not especially restricted when the polycarbodiimidecompound is added to the copolyester in the present invention, there arespecially preferably adopted methods for premixing the polycarbodiimidecompound with a polyester, for example, polytrimethylene terephthalateor polyethylene terephthalate at a high concentration, providing masterchips, then blending the chips and mixing the polycarbodiimide compoundwith the copolyester.

[0032] A monocarbodiimide compound in an amount within the range of 0.01to 3% by weight based on the copolyester may be further added when thepolycarbodiimide compound is added so as to melt spin the copolyesterand form the copolyester into the polyester fibers in the presentinvention. The amount of the added monocarbodiimide compound ispreferably within the range of 0.03 to 2% by weight, especiallypreferably within the range of 0.05 to 1% by weight.Bis(2,6-diisopropylphenyl)carbodiimide is most preferred as themonocarbodiimide compound from the viewpoint of the reactivity with thecopolyester.

[0033] The intrinsic viscosity of the copolyester formed into thepolyester fibers in the present invention is preferably 0.52 to 1.6.When the intrinsic viscosity is lower than 0.52, mechanicalcharacteristics of the copolyester are lowered and the strength of thefinally obtained fibers is liable to be insufficient. When the intrinsicviscosity exceeds 1.6, there is a tendency to lower the fluidity duringthe melting of the polymer and lower the moldability. The intrinsicviscosity of the copolyester is preferably within the range of 0.53 to1.5, more preferably within the range of 0.55 to 1.4.

[0034] The copolyester can be produced by a conventionally known method,and there can be adopted methods for subjecting, for example aterephthalic acid component, a 2,6-naphthlanedicarboxylic acid componentand a glycol component to esterification reaction or subjecting loweralkyl ester components of the terephthalic acid and the2,6-naphthlanedicarboxylic acid and the glycol component totransesterification in the presence of a transesterification catalyst,providing a bisglycol ester and/or a precondensate thereof and thensubjecting the resulting bisglycol and/or the precondensate thereof topolycondensation reaction in the presence of a polycondensation catalystand the like.

[0035] Solid-phase polymerization for raising the degree ofpolymerization or reducing the terminal carboxyl group content of thepolymer can preferably be carried out by a conventionally known method.

[0036] A small amount of an additive, for example, a lubricant, apigment, a dye, an antioxidant, a solid-phase polymerization promoter, afluorescent brightener, an antistatic agent, an antimicrobial agent, anultraviolet absorber, a light stabilizer, a heat stabilizer, a lightscreen or a delustering agent, if necessary, may be contained in thecopolyester used in the present invention.

[0037] The intrinsic viscosity of the polyester fibers of the presentinvention is preferably within the range of 0.5 to 1.5. When theintrinsic viscosity is within the range, mechanical strength of thefinally obtained fibers is sufficiently high and the handling isimproved. The intrinsic viscosity is more preferably within the range of0.52 to 1.4, especially preferably within the range of 0.55 to 1.3.

[0038] The terminal carboxyl group concentration of the polyester fibersof the present invention is preferably within the range of 15 eq/ton orbelow. When the terminal carboxyl group concentration is within therange, the resistance of the fibers to hydrolysis is more improved. Theterminal carboxyl group concentration is more preferably within therange of 12 eq/ton or below, especially preferably within the range of10 eq/ton or below.

[0039] The tensile strength of the polyester fibers of the presentinvention is preferably within the range of 1.5 to 4.5 cN/dtex. When thetensile strength is within the range, performances of the finallyobtained products are sufficient and handling is improved. The tensilestrength is more preferably within the range of 2.0 to 4.0 cN/dtex,especially preferably within the range of 2.5 to 3.5 cN/dtex.

[0040] When the polyester fibers of the present invention are produced,steps of melting spinning and drawing are not especially restricted, andthe polyester fibers can be produced with a conventionally known processfor producing usual polyester fibers. For example, methods for spinningthe polyester, then winding an undrawn yarn and separately drawing theundrawn yarn, methods for continuously drawing the undrawn yarn withoutwinding the undrawn yarn once, methods for melt spinning the polyester,then cooling and solidifying the undrawn yarn in a coagulation bath andsubsequently drawing the undrawn yarn under contact heating conditionssuch as in a heating medium or with a heated roller or the like or witha non-contact type heater or the like.

[0041] When the total draw ratio is set so as to be within the range of2.5 to 6.0 times in drawing the melt spun undrawn yarn, the resistanceto hydrolysis and tensile strength of the finally obtained fibers can bemade compatible at high levels, the yarn breakage ratio in a drawingstep is low and the productivity is more improved. The total draw ratiois more preferably within the range of 2.8 to 5.5 times, especiallypreferably within the range of 3.0 to 5.0 times.

[0042] The drawing step may be passed through only one-stage drawing ortwo or more drawing stages. When, for example, two-stage drawing isadopted, the draw ratio in the first stage may be 2.0 to 5.5 times, thedraw ratio in the second stage may be about 1.0 to 2.0 times and thetotal draw ratio may be adjusted to 2.5 to 6.0 times.

[0043] The shape of a spinneret used in spinning is not restricted whenthe polyester fibers of the present invention are produced, and any of acircular, a modified-cross section, a solid, a hollow forms and the likecan be adopted.

EXAMPLES

[0044] The present invention will be more specifically detailed byExamples hereinafter, but the Examples are not intended to limit thepresent invention at all. Respective values in the Examples weremeasured according the following methods:

[0045] (1) Intrinsic Viscosity:

[0046] Measurements were made by using o-chlorophenol as a solvent at35° C., and the intrinsic viscosity was determined from the relativeviscosity thereof according to the conventional method.

[0047] (2) Tensile Strength and Tensile Elongation:

[0048] Measurement was carried out according to the method described inJIS L1070.

[0049] (3) Terminal Carboxyl Group Concentration:

[0050] Measurements were made according to the method described inMakromol. Chem., 26, 226 (1958).

[0051] (4) Contents of Terephthalic Acid and 2,6-NaphthalenedicarboxylicAcid in Polymer:

[0052] A sample, together with an excessive amount of methanol, wassealed in a tube and subjected to decomposition with the methanol at260° C. for 4 hours in an autoclave, and the content of dimethylterephthalate and the content of dimethyl 2,6-naphthalenedicarboxylateof the resulting decomposition product were determined by using a gaschromatograph (HP6890 Series GC System, manufactured by HEWLETT PACKARDCO.) to determine the molar ratio of the terephthalic acid to the2,6-naphthalenedicarboxylic acid.

[0053] (5) Content of Trimethylene Glycol in Polymer:

[0054] A sample, together with an excessive amount of methanol, wassealed in a tube and subjected to decomposition with the methanol at260° C. for 4 hours in an autoclave, and the content of trimethyleneglycol and the content of dimethyl terephthalate of the decompositionproduct were determined by using the gas chromatograph (HP6890 Series GCSystem, manufactured by HEWLETT PACKARD CO.) to determine the molarratio of the trimethylene glycol based on the dimethyl terephthalate.

[0055] (6) Evaluation of Resistance to Hydrolysis:

[0056] An undrawn yarn was wet-heat treated under conditions of 130° C.,30 hours and 100% RH in an autoclave, and the lowering of intrinsicviscosity before and after the wet-heat treatment was measured toindicate the retention thereof in percentage. The retention ofresistance to hydrolysis which is the target of the present invention is90% or above.

[0057] (7) Evaluation of Resistance to Fatigue from Flexing:

[0058] The knot strength was measured according to the method describedin JIS L1070, and the percentage of the knot strength to the tensilestrength was calculated to make relative evaluation.

[0059] (8) Glass Transition Temperature:

[0060] A sample heated up to 260° C. at a heat-up rate of 10° C./min byusing DSC2010 Differential Scanning Calorimeter manufactured by TAInstruments Inc. as a differential scanning calorimeter (DSC) wasquenched in a test tube cooled to 0° C. and converted into an amorphousstate. The resulting sample was then heated up at a heat-up rate of 10°C./min to measure the midpoint glass transition point according to JISK7121.

Example 1

[0061] A reactor equipped with a stirrer, a rectifying column and amethanol distilling off condenser was charged with 90 parts of dimethylterephthalate, 12.6 parts of dimethyl 2,6-naphthalenedicarboxylate, 54.9parts of trimethylene glycol and 0.078 part of titanium tetrabutoxide asa catalyst, and transesterification was carried out while graduallyheating up the mixture from 140° C. and distilling off methanol producedas a result of the reaction to the outside of the system. The internaltemperature reached 210° C. in 3 hours after starting the reaction.

[0062] The resulting reaction product was then transferred to anotherreactor provided with a stirrer and a glycol distilling off condenser,and polymerization reaction was carried out while gradually heating upthe reaction product from 210° C. to 265° C. and reducing the pressurefrom atmospheric pressure to a high vacuum of 70 Pa. The melt viscosityof the reaction system was traced, and the polymerization reaction wasfinished when the intrinsic viscosity reached 0.75.

[0063] The molten polymer was extruded from the bottom of the reactorinto a strand state in cooling water, cut with a strand cutter andformed into chips.

[0064] The resulting chips were dried at 160° C. for 2 hours and thensubjected to solid-phase polymerization reaction at 200° C. under avacuum of 70 Pa and the flow of nitrogen gas by using tumbler typesolid-phase polymerization equipment. Table 1 shows the results of theintrinsic viscosity and terminal carboxyl group concentration of theobtained polymer.

[0065] The resulting polymer was melted and spun at a throughput of 14.3g/min and a takeoff speed of 400 m/min using an extrusion-spinningmachine equipped with a spinneret provided with 24 circular spinningholes having a hole diameter of 0.27 mm. The obtained undrawn yarn wasfed to a drawing treating machine equipped with a heating roller at 60°C. and a plate heater at 160° C. and subjected to drawing treatment at adraw ratio of 3.8 times to afford a 94 dtex/24-filament drawn yarn.Table 1 shows the results.

Example 2

[0066] Procedures were carried out in the same manner as in Example 1,except that the dicarboxylic acid component was changed into 70 parts ofdimethyl terephthalate and 37.7 parts of dimethyl2,6-naphthalenedicarboxylate in Example 1. Table 1 shows the results.

Example 3

[0067] Procedures were carried out in the same manner as in Example 1,except that the dicarboxylic acid component was changed into 50 parts ofdimethyl terephthalate and 62.9 parts of dimethyl2,6-naphthalenedicarboxylate in Example 1. Table 1 shows the results.

Example 4

[0068] Procedures were carried out in the same manner as in Example 1,except that the dicarboxylic acid component was changed into 20 parts ofdimethyl terephthalate and 100.6 parts of dimethyl2,6-naphthalenedicarboxylate in Example 1. Table 1 shows the results.

Example 5

[0069] Procedures were carried out in the same manner as in Example 1,except that the dicarboxylic acid component was changed into 125.7 partsof dimethyl 2,6-naphthalenedicarboxylate in Example 1. Table 1 shows theresults.

Comparative Example 1

[0070] A polyethylene terephthalate having an intrinsic viscosity of0.97 was melted at 285° C. and spun at a throughput of 12.8 g/min and atakeoff speed of 400 m/min by using an extrusion spinning machineequipped with a spinneret provided with 24 circular spinning-holeshaving a hole diameter of 0.27 mm. The resulting undrawn yarn was fed toa drawing treating machine equipped with a heating roller at 85° C. anda plate heater at 160° C. and subjected to drawing treatment at a drawratio of 4.3 times to afford a 93 dtex/24-filament drawn yarn. Table 1shows the results.

Comparative Example 2

[0071] Procedures were carried out in the same manner as in Example 1,except that the dicarboxylic acid component was changed into only 100parts of dimethyl terephthalate to provide a polytrimethyleneterephthalate homopolymer in Example 1. Table 1 shows the results.

Example 6

[0072] A reactor equipped with a stirrer, a rectifying column and amethanol distilling off condenser was charged with 100 parts of dimethylterephthalate, 49.4 parts of trimethylene glycol, 10.4 parts of1,4-cyclohexanedimethanol and 0.078 part of titanium tetrabutoxide as acatalyst, and transesterification was carried out while graduallyheating up the mixture from 140° C. and distilling off methanol producedas a result of the reaction to the outside of the system. The internaltemperature reached 210° C. in 3 hours after starting the reaction.

[0073] The resulting reaction product was then transferred to anotherreactor provided with a stirrer and a glycol distilling off condenser,and polymerization reaction was carried out while gradually heating upthe reaction product from 210° C. to 265° C. and reducing the pressurefrom the atmospheric pressure to a high vacuum of 70 Pa. The meltviscosity of the reaction system was traced, and the polymerizationreaction was finished when the intrinsic viscosity reached 0.75.

[0074] The molten polymer was extruded from the bottom of the reactorinto a strand state in cooling water, cut with a strand cutter andformed into chips.

[0075] The resulting chips were dried at 160° C. for 2 hours and thensubjected to solid-phase polymerization reaction at 200° C. under avacuum of 70 Pa and the flow of nitrogen gas. Table 1 shows the resultsof the intrinsic viscosity and terminal carboxyl group concentration ofthe obtained polymer.

[0076] The resulting polymer was melted at 265° C. and spun at athroughput of 14.5 g/min and a takeoff speed of 400 m/min by using anextrusion spinning machine equipped with a spinneret provided with 24circular spinning holes having a hole diameter of 0.27 mm. The obtainedundrawn yarn was fed to a drawing treating machine equipped with aheating roller at 60° C. and a plate heater at 160° C. and subjected todrawing treatment at a draw ratio of 3.8 times to afford a 95dtex/24-filament drawn yarn. Table 1 shows the results.

Example 7

[0077] Procedures were carried out in the same manner as in Example 6,except that the glycol component was changed into 43.9 parts oftrimethylene glycol and 20.8 parts of 1,4-cyclohexanedimethanol inExample 6. Table 1 shows the results.

Example 8

[0078] Procedures were carried out in the same manner as in Example 6,except that the glycol component was changed into 16.5 parts oftrimethylene glycol and 72.7 parts of 1,4-cyclohexanedimethanol inExample 6. Table 1 shows the results. TABLE 1 (1) (2) (3) (4) (5) (6)(7) (8) (9) (5) (6) (10) (11) (12) (13) (14) Ex. 1 PTT 1.01 11  90/10100/0 47 0.93 16 94 4.5 30 92 83 Ex. 2 PTT 0.95 13  70/30 100/0 53 0.8817 95 4.7 32 95 80 Ex. 3 (15) 0.94 12  50/50 100/0 63 0.86 18 93 4.6 3396 78 Ex. 4 PTN 0.91 14  20/80 100/0 74 0.82 19 93 4.8 25 99 76 Ex. 5PTN 0.90 14  0/100 100/0 83 0.84 20 92 5.2 20 100 75 Ex. 6 PTT 1.02 9100/0  92/8 49 0.94 16 95 4.5 35 95 88 Ex. 7 PTT 1.01 10 100/0  75/25 560.93 15 95 4.4 36 97 85 Ex. 8 PCT 0.97 12 100/0  22/78 84 0.90 17 93 4.730 99 80 (16) PET 0.97 8 100/0 −(18) 76 0.87 15 93 6.1 20 62 70 (17) PTT1.00 10 100/0 100/0 44 0.93 17 95 4.5 37 85 90

Example 9

[0079] A reactor equipped with a stirrer, a rectifying column and amethanol distilling off condenser was charged with 90 parts of dimethylterephthalate, 12.6 parts of dimethyl 2,6-naphthalenedicarboxylate, 70parts of trimethylene glycol and 0.053 part of titanium tetrabutoxide asa catalyst, and transesterification was carried out while graduallyheating up the mixture from 140° C. and distilling off methanol producedas a result of the reaction to the outside of the system. The internaltemperature reached 210° C. in 3 hours after starting the reaction.

[0080] The resulting reaction product was then transferred to anotherreactor provided with a stirrer and a glycol distilling off condenser,and polymerization reaction was carried out while gradually heating upthe reaction product from 210° C. to 265° C. and reducing the pressurefrom atmospheric pressure to a high vacuum of 70 Pa. The melt viscosityof the reaction system was traced, and the polymerization reaction wasfinished when the intrinsic viscosity reached 0.75.

[0081] The molten polymer was extruded from the bottom of the reactorinto a strand state in cooling water, cut with a strand cutter andformed into chips.

[0082] The resulting chips were dried at 130° C. for 5 hours and thensubjected to solid-phase polymerization reaction at 190° C. under avacuum of 70 Pa and the flow of nitrogen gas by using tumbler typesolid-phase polymerization equipment. Table 2 shows the results of theintrinsic viscosity and terminal carboxyl group concentration of theobtained chips. A 5 wt. % dichloromethane solution of 2,2′-bisoxazolinewas added from a side feeder at a rate so as to provide the amountmentioned in Table 3, mixed with the resulting chips, then melted at255° C. and spun at a throughput of 14.5 g/min and a takeoff speed of400 m/min by using an extrusion spinning machine equipped with aspinneret provided with 24 circular spinning holes having a holediameter of 0.27 mm. The obtained undrawn yarn was fed to a drawingtreating machine equipped with a heating roller at 60° C. and a plateheater at 160° C. and subjected to drawing treatment at a draw ratio of75% of the maximum draw ratio to afford a drawn yarn. Table 3 shows theresults.

Example 10

[0083] Procedures were carried out in the same manner as in Example 9,except that 126 parts of dimethyl 2,6-naphthalenedicarboxylate was usedas the dicarboxylic acid component, the intrinsic viscosity before thesolid-phase polymerization was 0.65 and a heating roller at 85° C. wasused in Example 9. Tables 2 and 3 show the results.

Example 11

[0084] Procedures were carried out in the same manner as in Example 9,except that the glycol component was changed into 62 parts oftrimethylene glycol and 20 parts of 1,4-cyclohexanedimethanol in Example9. Tables 2 and 3 show the results.

Example 12

[0085] Procedures were carried out in the same manner as in Example 9,except that the glycol component was changed into 25 parts oftrimethylene glycol and 55 parts of 1,4-cyclohexanedimethanol in Example9. Tables 2 and 3 show the results.

Example 13

[0086] Procedures were carried out in the same manner as in Example 9,except that chips dried at 130° C. for 5 hours without carrying out thesolid-phase polymerization were used and melt spun in Example 9. Tables2 and 3 show the results.

Comparative Example 3

[0087] Procedures were carried out in the same manner as in Example 9,except that the dicarboxylic acid component was 100 parts of dimethylterephthalate in Example 9. Tables 2 and 3 show the results.

Example 14

[0088] A reactor equipped with a stirrer, a rectifying column and amethanol distilling off condenser was charged with 90 parts of dimethylterephthalate, 12.6 parts of dimethyl 2,6-naphthalenedicarboxylate, 70parts of trimethylene glycol and 0.053 part of titanium tetrabutoxide asa catalyst, and transesterification was carried out while graduallyheating up the mixture from 140° C. and distilling off methanol producedas a result of the reaction to the outside of the system. The internaltemperature reached 210° C. in 3 hours after starting the reaction.

[0089] The resulting reaction product was then transferred to anotherreactor provided with a stirrer and a glycol distilling off condenser,and polymerization reaction was carried out while gradually heating upthe reaction product from 210° C. to 265° C. and reducing the pressurefrom atmospheric pressure to a high vacuum of 70 Pa. The melt viscosityof the reaction system was traced, and the polymerization reaction wasfinished when the intrinsic viscosity reached 0.75.

[0090] The molten polymer was extruded from the bottom of the reactorinto a strand state in cooling water, cut with a strand cutter andformed into chips.

[0091] The resulting chips were dried at 130° C. for 5 hours and thensubjected to solid-phase polymerization reaction at 190° C. under avacuum of 70 Pa and the flow of nitrogen gas by using tumbler typesolid-phase polymerization equipment. Table 2 shows the results of theintrinsic viscosity and terminal carboxyl group concentration of theobtained chips.

[0092] The resulting chips were subjected to chip blending withpolycarbodiimide master chips [polyethylene terephthalate chipscontaining 15% by weight ofpoly(2,4,6-triisopropylphenyl)-1,3-carbodiimide component] in the amountmentioned in Table 3, and the blended chips were then melted at 255° C.and spun at a throughput of 14.5 g/min and a takeoff speed of 400 m/minby using an extrusion spinning machine equipped with a spinneretprovided with 24 circular spinning holes having a hole diameter of 0.27mm. The obtained undrawn yarn was fed to a drawing treating machineequipped with a heating roller at 60° C. and a plate heater at 160° C.and subjected to drawing treatment at a draw ratio of 75% of the maximumdraw ratio to afford a drawn yarn. Table 3 shows the results.

Example 15

[0093] Procedures were carried out in the same manner as in Example 14,except that the dicarboxylic acid component was changed into 126 partsof dimethyl 2,6-naphthalenedicarboxylate, the intrinsic viscosity beforethe solid-phase polymerization was 0.65 and a heating roller at 85° C.was used in Example 14. Tables 2 and 3 show the results.

Example 16

[0094] Procedures were carried out in the same manner as in Example 14,except that the dicarboxylic acid component was 100 parts of dimethylterephthalate and the glycol component was changed into 62 parts oftrimethylene glycol and 20 parts of 1,4-cyclohexanedimethanol in Example14. Tables 2 and 3 show the results.

Example 17

[0095] Procedures were carried out in the same manner as in Example 14,except that the dicarboxylic acid component was 100 parts of dimethylterephthalate and the glycol component was changed into 25 parts oftrimethylene glycol and 55 parts of 1,4-cyclohexanedimethanol in Example14. Tables 2 and 3 show the results.

Example 18

[0096] Procedures were performed in the same manner as in Example 14,except that the solid-phase polymerization was not carried out inExample 14. Tables 2 and 3 show the results.

Example 19

[0097] Procedures were carried out in the same manner as in Example 14,except that molten bis(2,6-diisopropylphenyl)carbodiimide was added froma side feeder at a rate so as to provide the amount mentioned in Table 3at 75° C. to the blended chips by using an extrusion spinning machineequipped with a spinneret provided with 24 circular spinning holeshaving a hole diameter of 0.27 mm in Example 14. Tables 2 and 3 show theresults. TABLE 2 Physical Property of Copolyester Composition (1) (2)(3) (4) (5) (6) (7) (6) (7) Ex. 9 PTT  90/10 100/0 0.75 23 1.05 12 Ex.10 PTN  0/100 100/0 0.65 19 0.94 10 Ex. 11 PTT 100/0  80/20 0.75 21 1.03 9 Ex. 12 PTT/PCT 100/0  42/58 0.75 18 1.01  8 Ex. 13 PTT  90/10 100/00.75 23 — — Ex. 14 PTT  90/10 100/0 0.75 20 1.05 12 Ex. 15 PTN  0/100100/0 0.65 19 0.94 10 Ex. 16 PTT 100/0  80/20 0.75 12 1.03  9 Ex. 17PTT/PCT 100/0  42/58 0.75 18 1.01  8 Ex. 18 PTT 100/0 100/0 0.75 23 — —Ex. 19 PTT  90/10 100/0 0.75 23 1.07 11 (8) PTT 100/0 100/0 0.75 23 1.0711

[0098] TABLE 3 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)(14) Ex. 9 0.1 — — 3.9 1.09 5 93 4.7 31 95 85 Ex. 10 0.2 — — 3.6 1.01 6100 5.4 19 100 78 Ex. 11 0.2 — — 3.6 1.12 5 101 4.6 37 99 88 Ex. 12 0.1— — 3.7 1.04 4 98 4.5 39 97 81 Ex. 13 0.5 — — 3.5 0.99 9 104 4.4 35 9887 Ex. 14 — 0.3 — 3.8 0.98 6 95 4.3 33 97 84 Ex. 15 — 0.5 — 3.5 0.89 6104 5.0 22 100 76 Ex. 16 — 0.5 — 3.6 0.96 5 104 4.4 34 98 85 Ex. 17 —0.3 — 3.6 0.97 6 101 4.4 35 96 80 Ex. 18 —  0.75 — 3.6 0.90 8 101 4.5 3590 88 Ex. 19 — 0.3 0.3 3.5 1.01 8 104 4.6 30 96 82 (15) — — — 3.6 0.9118 100 4.3 39 80 92

INDUSTRIAL APPLICABILITY

[0099] According to the present invention, there can be providedpolyester fibers which have resistances to both hydrolysis and fatiguefrom flexing at high levels and can usefully be utilized forapplications requiring long-term and continuous use at high temperatureand humidity such as papermaking canvas, tire cord, sterilized fabricsand the like and the industrial significance of the polyester fibers isgreat.

1. Polyester fibers comprising a copolyester which simultaneouslysatisfies the following respective requirements (a) to (c), (a) aterephthalic acid component in an amount of 0 to 100 mol % and a2,6-naphthalenedicarboxylic acid component in an amount of 100 to 0 mol% respectively based on the whole dicarboxylic acid component, whereinthe total amount, of the terephthalic acid component and the2,6-naphthalenedicarboxylic acid component, accounts for 90 mol % ormore based on the whole dicarboxylic acid component, (b) a trimethyleneglycol component accounts for 22 to 100 mol % and a1,4-cyclohexanedimethanol component accounts for 78 to 0 mol %respectively based on the whole glycol component, wherein the totalamount, of the trimethylene glycol component and the1,4-cyclohexanedimethanol component, accounts for 90 mol % or more basedon the whole glycol component and (c) the sum total value of mol % ofthe 2,6-naphthalenedicarboxylic acid component and mol % of the1,4-cyclohexanedimethanol component is 2 mol % or more.
 2. The polyesterfibers according to claim 1, wherein the glass transition temperature ofthe copolyester is 45° C. or above.
 3. The polyester fibers according toclaim 1, wherein the polyester fibers comprise a copolyester having aterminal carboxyl group concentration of 30 eq/ton or below.
 4. Thepolyester fibers according to claim 1, wherein the polyester fibers areobtained by adding a bisoxazoline compound in an amount of 0.05 to 5% byweight based on the copolyester to the copolyester, by uniformly mixingthe bisoxazoline compound with the copolyester and then by carrying outmelt spinning and have a terminal carboxyl group concentration of 15eq/ton or below.
 5. The polyester fibers according to claim 4, whereinthe bisoxazoline compound is 2,2′-bis(2-oxazoline).
 6. The polyesterfibers according to claim 1, wherein the polyester fibers are obtainedby adding a polycarbodiimide compound in an amount of 0.05 to 5% byweight based on the copolyester to the copolyester, by uniformly mixingthe polycarbodiimide compound with the copolyester and then by carryingout melt spinning, and have a terminal group concentration of 15 eq/tonor below.
 7. The polyester fibers according to claim 6, wherein thepolycarbodiimide compound is poly(2,4,6-triisopropylphenyl)-1,3-carbodiimide.
 8. The polyester fibers according to claim 6, whereina monocarbodiimide compound in an amount of 0.01 to 3% by weight basedon the copolyester is further added to the copolyester.
 9. The polyesterfibers according to claim 8, wherein the monocarbodiimide compound isbis(2,6-diisopropylphenyl)carbodiimide.